Duration window in status bar sometimes shows 0:00 when there is 45-60 minutes of audio

Unfortunately I do not know what sequence of events leads to this, but while editing audio of around 45-60 minutes in length I will on rare occassions notice that the status bar is showing a duration of 0:00.

UPDATE: I was paying more attention to the sequence of events tonight and discovered that this happens when I convert the audio sample type from 44.1 KHZ at 32 bit to 44.1 KHZ at 16 bit. When I do that, the duration window in the status bar drops to 0:00.000 when is actually should show 47:57.618.